1. Field of the Invention
This invention relates to the drilling of side tracks from a main wellbore, and more particularly, to the use of hydrajetting to cut a window in the well casing prior to drilling, thereby facilitating the drilling operation and providing a desired window shape and size. This allows a fit for subsequent tools or casing strings to be inserted through this window.
2. Description of the Prior Art
Many wells today have a deviated bore or side track drilled extending away at an angle from a generally vertical main wellbore. The drilling of such a side track is accomplished by several steps. After casing the main wellbore, a multi-stage milling process is utilized to laterally cut a window through the casing at the general location where it is desired to start the side track. Once the window is milled open, the drilling process may begin. The problem is that casing is made of hard steel, and it is very common for the drill bit to chatter on the steel. This can cause drill breakage and/or produce erratic cutting of the window. Typically, the window is a relatively long, elongated opening, preferably somewhat teardrop shaped, and cutting the window is very time consuming and correspondingly expensive.
There is a need, therefore, for apparatus and methods of cutting windows which can be accomplished more quickly and less expensively and also in a manner assuring a more precise cut of the casing.
The present invention solves this problem by providing for the use of hydrajetting to cut, or at least partially cut, the window in the casing. After the window is more precisely cut using this method, drilling of the actual side track is carried out more quickly and with fewer problems.